This application bases priority on International Application No. PCT/DE01/00108, filed Jan. 12, 2001, which in turn bases priority on German Application No. DE 100 03 562.0, filed Jan. 27, 2000.
1. Field of the Invention
The invention relates to a device and method for sorting out or extracting metal fractions from a bulk material stream.
2. Description of the Prior Art
It is necessary to sort out or separate metal fractions from the most varied bulk material streams. In the simplest case they are constituted by crown corks of beer bottles and aluminum parts from a broken glass bulk material stream. However, it is also necessary to sort on the basis of their different metal and non-metal fractions, non-homogeneous bulk material streams, e.g. shredded car parts. In particular, the stainless steel fraction has to be separated from other fractions. In the same way as nonferrous metals, stainless steel is not very ferromagnetic.
Such a method is described in DE-A1-35 13 664, in which an inductance-variable detector coil on a refuse chute controls a compressed air nozzle, which blows away nonferrous metals. Quite apart from the limited local resolution, which is just sufficient for the detection of aluminum cans, the problem arises that varying inductance changes for different materials and also different object sizes do not allow clear information to be provided with regards to the optimum blow-out point. It is always only possible to blow out a specific fraction and not, if different compositions exist, the smaller fraction for whose blowing out only reduced costs are involved.
It is impossible to blow out non-metals, although this is highly desirable in the case of crushed car scrap.
As a result of saturation effects, particles bringing about a strong inductance change can desensitize the coil for such a long time that it is necessary to accept a significant level of incorrect sorting or extremely slow feed rates.
Methods of the type described, e.g. in DE-A1-40 14 969 are consequently not very suitable for correctly detecting metal and for the different handling of different metal fractions.
The parallel detection of both the color and the presence of metal requires a considerable amount of time which, as described in DE-A1-40 17 129, gives rise to slow bulk material conveying rates.
Other proposals, such as e.g. those of DE-A1-42 35 956, in which the fine surface structure of the materials are determined by bombarding with electromagnetic waves, are much too complicated and costly during evaluation, and require a time-consuming logic consideration. In addition, proposals have already been made for increasing the separation efficiency of material mixtures, such as e.g. in German utility model DE-U-93 09 786.
Finally, DE-A1-40 17 274 describes an apparatus for detecting and separating metal particles, in which different down pipes are provided with detector coils, which in each case control a flap mechanism for deflecting fluid bulk material. In the case of shredded material, e.g. car scrap, unavoidably there are certain parts which are well above the nominal size, and which would immediately block such pipes. However, even in the case of bulk material such pipes tend to become blocked.
It is also desirable, as a function of the bulk material to be sorted, to be able to readjust the separation efficiency in order to take account of different bulk material prerequisites and enable the sorting out of the in each case desired fractions.
Thus, it is e.g. known that there can be considerable differences in shredded car scrap as a function of the country of origin. Whereas, European car scrap contains a large amount of light alloys and plastic parts, in the scrap from U.S. cars, there are far more stainless steel parts, whose sorting out is correspondingly worthwhile.
It is also known that the size and shape of the parts to be sorted are dependent on the nature of the shredding machine, quite apart from the materials used in the vehicles. However, once a first batch has been supplied by a particular preprocessing plant, it is generally to be assumed that over a long period (the next years), parts with a similar size and shape will arrive and the sorting parameters when operating the sorting apparatus, consequently, remain substantially the same.
The problem of the invention is to provide a method and apparatus for sorting out such metal fractions, sorting out having to take place rapidly and also reliably in the case of larger parts.
Specifically, in the case of larger parts, it is necessary to control the blow-out nozzles in such a way that the parts are correctly blown out, because too sort or too early blowing (such as arises with large objects through a premature response of the prior art metal detectors) will not lead to the parts being correctly brought into a new trajectory. In the case of shredders, there are also many elongated parts, which are difficult to blow out.
According to the invention, this problem is solved by the features of the main claim. The subclaims provide advantageous embodiments of the invention.
It is in particular advantageous that as a result of the inventive arrangement of an electromagnetic sensor below advantageously a horizontally directed conveyor belt, it is not only possible to determine the digital signal metal (YES/NO), but also a signal pattern from whose details, particularly its edge rise, conclusions can if necessary be drawn concerning the size and the material of the individual parts.
As a result of the position of the essentially flat parts on the conveyor belt, it is possible to consider the distance between the mass center and the sensor to be identical for all the parts.
By means of the sensor described in the second part of the description relative to the drawings, it is possible to generate eddy currents in a metal part to be separated, particularly an aluminum or stainless steel part, which in turn builds up a magnetic field acting in opposition to the excitation field. As a result of the buildup of the field, but in particular through line losses to which the eddy currents are exposed in the metal, an energy loss is brought about in the field-generating sensor, which as damping of said oscillator is in order for the size, spacing and dimensions of the object. The individual particles to be sorted out are slightly heated by the eddy currents.
Admittedly, use has already been made of the generation of opposing fields by eddy currents, induced by very strong fields in order to deflect from the trajectory in which the rotational fields arise, but this deflection is determined by the geometry of the object and the eddy currents flowing in said object and less by the actual material, and is not of an optimum nature in its directional component.
However, the invention xe2x80x9cmissesxe2x80x9d the particle and controls a blow-out nozzle bar, which provides the particle with a suitable air stream for ejection during a drop section, which e.g. follows a horizontally directed conveyor belt. Thus, for the selected particles an always identical trajectory is much more reliably ensured than by a very strong field, which induces eddy currents in all the objects with a different intensity for ejection purposes.
In addition, the invention makes it possible to mathematically evaluate the data detected for an object, namely the size, the strength of the eddy current caused (the steepness of an edge rise in the signal pattern enabling conclusions to be drawn thereon), in which the strength of the back-indication of the object, i.e. either its weight or in the case of comparable weights of the particles its material, 1) can be determined by mathematical integration over the surface area of a xe2x80x9cpeakxe2x80x9d, or which can be easily implemented from the apparatus standpoint in the plant by, 2) can be taken into account by modifying the distance from the changed sensor and the bulk material stream, so that in both cases, the response limits for separation can be easily changed.
A major advantage is provided by the optional, optical determination of the particles on the belt or at the start of the drop section, because it provides the possibility of more precise positional information to blow against the centers of gravity of the particles by means of the air nozzles which are provided with precisely determined action points and much more densely provided than the coils, so as to bring about an optimum trajectory change.
Through a plurality of sensors, which can be juxtaposed at right angles to the bulk material stream, it is possible to monitor the entire bulk material stream and provide a further metal/no metal information concerning the optically detected objects, and in the case of an adequate separation efficiency, to permit a decision to be made concerning the nature of the metal by means of the object size and sensor information.
As the field distribution of any LC sensor coil drops strongly towards the edge, it is proposed that there are at least two mutually displaced rows.
The invention also proposes, in addition to the sensors equidistantly spaced with respect to the bulk material stream, the provision of further sensors with different spacings with respect to said stream, so as in this way to detect fractions with significantly different response ranges in the bulk material stream, and consequently permit the sorting out of certain fractions between the upper and lower limits.
However, it is also possible to provide additional optoelectronics sensors, which can qualify the signals obtained from the electromagnetic detection with optoelectronically detected signals, i.e. for example the size and color of the object.
Another advantage of the invention is the possibility of logical reversal, i.e. either the blowing out of utilizable metal fractions or the blowing out of utilizable plastic fractions, as a function of which provides the desired, marketable fraction in the most type-pure form.